Power management in tunneled direct link setup

ABSTRACT

A method and apparatus of managing power save in a wireless network is provided. A direct link with a peer station (STA) is established by exchanging a Tunneled Direct Link Setup (TDLS) setup request frame and a TDLS setup response frame through an access point (AP). The peer STA enters power save mode (PSM). Traffic data that are destined for the peer STA in the PSM are buffered and a peer traffic indication (PTI) frame is transmitted to the peer STA in the PSM. The PTI frame includes a traffic identifier (TID) field and a sequence control field. Unnecessary allocation of service period can be prevented.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/062,944, filed on Apr. 22, 2011, now U.S. Pat. No. 8,279,757, whichis the National Stage filing under 35 U.S.C. §371 of InternationalApplication No. PCT/KR2009/005156, filed on Sep. 11, 2009, which claimsthe benefit of U.S. Provisional Application No. 61/096,292, filed onSep. 11, 2008, the contents of all of which are hereby incorporated byreference herein in their entireties.

TECHNICAL FIELD

The present invention relates to a wireless local area network (WLAN),and more particularly, to a method and apparatus of managing power savesupporting a tunneled direct link setup (TDLS) in a WLAN system.

BACKGROUND ART

With development of information communication technologies, a variety ofwireless communication technologies have been developed. A wirelesslocal area network (WLAN) is a technology permitting wireless access toInternet in specific service areas such as home or companies or airplanes by the use of portable terminals such as a personal digitalassistant (PDA), a laptop computer, and a portable multimedia player(PMP) on the basis of a radio frequency technology.

These days, thanks to the increased availability of WLANs, portableterminal users such as laptop computer users are able to perform theirtasks with increased mobility. For example, a user can take his laptopcomputer from his desk into a conference room to attend a meeting andstill have access to his local network to retrieve data and have accessto the Internet via one or more modems or gateways present on the localnetwork without being tethered by a wired connection. Similarly,business travelers commonly use their portable terminals to gain accessto their email accounts, to check if there is any unread email, and toread and send email.

In the initial WLAN stage, a data rate of 1 to 2 Mbps was supported bythe use of frequency hopping, spread spectrum, and infraredcommunication using a frequency of 2.4 GHz. In recent years, with thedevelopment of the wireless communication technology, a data rate of 54Mbps can be supported by applying the orthogonal frequency divisionmultiplex (OFDM) technology, etc. to the WLAN. In addition, the WLAN hasdeveloped or is developing wireless communication technologies forimprovement in quality of service (QoS), compatibility of an accesspoint (AP) protocol, security enhancement, wireless resourcemeasurement, wireless access in vehicular environment, fast roaming,mesh network, inter-working with external networks, wireless networkmanagement, and the like.

In the system based on Institute of Electrical and Electronics Engineers(IEEE) 802.11 standard, a basic service set (BSS) means a set ofstations (STAs) successfully synchronized. A basic service area (BSA)means an area including members of the BSS. The BSA can vary dependingon propagation characteristics of a wireless medium. The BSS can bebasically classified into two kinds of an independent BSS (IBSS) and aninfrastructured BSS. The former means a BSS that constitutes aself-contained network and that is not permitted to access adistribution system (DS). The latter means a BSS that includes one ormore access points (APs) and a distribution system and that uses the APsin all the communication processes including communications between thestations.

Before the IEEE 802.11e standard which is published on 11Nov. 2005 andis incorporated by reference, the infrastructured BSS required totransmit data necessarily through the AP without permitting the directtransmission of data between non-AP stations (non-AP STAs). STAs are notallowed to transmit frames directly to other STAs in a BSS and shouldalways rely on the AP for the delivery of the frames. The IEEE 802.11estandard agreed a direct link setup (DLS) between the non-AP STAs toimprove the efficiency of WLAN. A QBSS is a BSS supporting quality ofservice (QoS). A QSTA is a STA supporting QoS. A legacy STA is a STA notsupporting QoS. A QAP is a AP supporting QoS. The QBSS includes QSTAsand one or more QAPs. QSTAs may transmit frames directly to another QSTAby setting up such data transfer using DLS. Non-AP QSTAs can set up adirect link and directly communicate with each other through the directlink. The direct link is a unidirectional link from one non-AP QSTA toanother non-AP QSTA operating in the same infrastructure QBSS that doesnot pass through a QAP. Once the direct link has been set up, all framesbetween the two non-AP QSTAs are exchanged directly.

To set up the direct link, the two non-AP QSTAs exchanges a DLS requestframe and a DLS response frame via the QAP. This means setting up DLSrely on the QAP. The WLAN system currently used is generally based onthe IEEE 802.11a/b/g standard. This means QBSS is not the basic BSS. Thenon-AP STAs may be QSTAs supporting the QoS but the AP may be a legacyAP not supporting the QoS. As a result, non-AP QSTA cannot utilize theDLS service since legacy APs cannot support the DLS service.

STAs can operate in one of two power management modes of an active mode(AM) and a power save mode (PSM). Since the non-AP STA is generally auser's portable device, it is necessary to support the PSM so as toeffectively manage the power. In the IEEE 802.11e standard, powermanagement is called as automatic power save delivery (APSD). The APSDdefines two delivery mechanisms, namely unscheduled APSD (U-APSD) andscheduled APSD (S-APSD).

In the direct link, power management is also needed. IEEE 802.11estandard provides APSD support in the QBSS. After establishing DLS, oneQSTA in AM or PSM transmits a data frame and/or a management frame tothe other QSTA in PSM or AM via the direct link. But when non-AP QSTAsand a legacy AP are co-exists, IEEE 802.11e standard does not disclosehow to establish the direct link and how to manage PSM.

DISCLOSURE OF INVENTION Technical Problem

The present invention provides a method and apparatus of powermanagement in a wireless network supporting TDLS.

The present invention also provides a method and apparatus of powermanagement in a TDLS link to improve efficiency of radio resources.

Solution to Problem

In an aspect, a method of managing power save in a wireless network isprovided.

The method includes establishing a direct link with a peer station (STA)by exchanging a Tunneled Direct Link Setup (TDLS) setup request frameand a TDLS setup response frame through a access point (AP), receivingan indicator indicating that the peer STA enters power save mode (PSM)via the direct link, buffering traffic data that are destined for thepeer STA in the PSM, and transmitting a peer traffic indication (PTI)frame to the peer STA in the PSM. The PTI frame indicates a state of aframe buffer for the peer STA. The PTI frame includes a trafficidentifier (TID) field that indicates the highest TID for which the peerSTA has buffered traffic.

The PTI frame may further include a sequence control field that is setto the sequence number of the latest traffic data transmitted to thepeer STA from the TID indicated in the TID field. The PTI frame mayfurther include a AC traffic available field indicating a non-emptyaccess category (AC). The PTI frame may further include information thatidentifies the direct link.

The indicator may be a power management field in a frame control fieldof a frame and the peer STA enter the PSM by setting the powermanagement field.

The method further includes receiving a trigger frame from the peer STAas a response of the PTI frame, the trigger frame indicating that thepeer STA is in active mode.

The TDLS setup request frame and a TDLS setup response frame may beencapsulated in data frames in order to allow the TDLS setup requestframe and a TDLS setup response frame to be transmitted through the APtransparently.

In another aspect, a method of managing power save in a wireless networkis provided. The method includes establishing a direct link with a peerstation (STA) by exchanging a Tunneled Direct Link Setup (TDLS) setuprequest frame and a TDLS setup response frame through a access point(AP), entering power save mode (PSM) by notifying the peer STA throughthe direct link, and changing power management mode from the PSM toactive mode when a peer traffic indication (PTI) frame is received fromthe peer STA, the PTI frame indicating a state of a frame buffer whichis buffered by the peer STA. The PTI frame includes a traffic identifier(TID) field that indicates the highest TID for which the peer STA hasbuffered traffic.

In still another aspect, an apparatus supporting TDLS includes a radiofrequency (RF) unit to transmit and receive radio signals, and aprocessor operatively coupled with the RF unit. The processor isconfigured to establish a direct link with a peer station (STA) byexchanging a Tunneled Direct Link Setup (TDLS) setup request frame and aTDLS setup response frame through a access point (AP), receive anindicator indicating that the peer STA enters power save mode (PSM) viathe direct link, buffer traffic data that are destined for the peer STAin the PSM, and transmit a peer traffic indication (PTI) frame to thepeer STA in the PSM, the PTI frame indicating a state of a frame bufferfor the peer STA. The PTI frame includes a traffic identifier (TID)field that indicates the highest TID for which the peer STA has bufferedtraffic.

In still another aspect, an apparatus supporting TDLS includes a radiofrequency (RF) unit to transmit and receive radio signals, and aprocessor operatively coupled with the RF unit. The processor isconfigured to establish a direct link with a peer station (STA) byexchanging a Tunneled Direct Link Setup (TDLS) setup request frame and aTDLS setup response frame through a access point (AP), enter power savemode (PSM) by notifying the peer STA through the direct link, and changepower management mode from the PSM to active mode when a peer trafficindication (PTI) frame is received from the peer STA, the PTI frameindicating a state of a frame buffer which is buffered by the peer STA.

Advantageous Effects of Invention

During power management through a TDLS direct link, utilization of radioresources can be improved. Unnecessary allocation of service period canbe prevented.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a WLAN system for implementing embodiments of thepresent invention.

FIG. 2 is a diagram illustrating an example of a TDLS frame.

FIG. 3 is a diagram illustrating a communication method according to anembodiment of the present invention.

FIG. 4 is a diagram illustrating a problem due to invalid PTItransmission.

FIG. 5 is a block diagram of an apparatus for wireless communication toimplement an embodiment of the present invention is implemented.

BEST MODE FOR CARRYING OUT THE INVENTION

Exemplary embodiments of the present invention will now be described indetail with reference to the accompanying drawings. In the followingdescription, a wireless local area network (WLAN) system as a wirelesscommunication system will be taken as an example. But this is merelyillustrative and the present invention can be applicable in the samemanner to any other wireless communication systems besides the WLANsystem except for a case not allowed in terms of its properties. Termsor words unique to the WLAN system used in the embodiments of thepresent invention may be properly changed to other terms or wordscommonly used in a corresponding wireless communication system.

FIG. 1 illustrates a WLAN system for implementing embodiments of thepresent invention. The WLAN system includes one or more basic servicesets (BSSs). The BSS refers to a set of stations (STA) that cancommunicate with each other in synchronization, which does not indicatea particular area. The BSS may be classified into an infrastructure BSSand an independent BSS (IBSS). FIG. 1 shows the infrastructure BSS. Theinfrastructure BSS include one or more STAs. A first BSS BSS1 includesSTA110, and STA2 20. A second BSS BSS2 includes STA3 30, STA4 40 andSTA5 50. In each infrastructure BSS, at least one access point (AP) mayexist. The AP is a station for providing a distribution service. TheSTA2 20 in the first BSS BSS1 may be a AP1 and the STA5 50 in the firstBSS BSS2 may be a AP2. A distribution system (DS) 80 connects aplurality of APs (AP1 and AP2). Meanwhile, the IBSS, not including anAP, includes STAs, all of which are mobile stations, and forms aself-contained network without allowing a connection to the DS 80.

The STA is a certain function medium including a medium access control(MAC) following the stipulation of IEEE 802.11 standard and a physicallayer interface with respect to a wireless medium. The STA may be calledas a node. The STA may be an AP or non-AP.

Non-AP STAs (STA1 10, STA3 30, STA4 40, STA6 60, STAT7 70, and STA8 80)may be a mobile terminal manipulated by a user. The non-AP STA may bereferred to by other names such as wireless transmit/receive unit(WTRU), user equipment (UE), mobile station (MS), mobile terminal (MT),mobile subscriber unit, or the like.

The APs (AP1 and AP2) provide an access to the DS 80 by way of awireless medium for STAs associated thereto. In the infrastructure BSSincluding the AP, communication between non-AP STAs is made by way ofthe AP, but when a direct link has been established, the non-AP STAs candirectly communicate with each other. The AP may be also called by othernames such as centralized controller, base station (BS), node-B, basetransceiver system (BTS), site controller, and the like.

A plurality of infrastructure BSSs may be connected via the DS 80. Theplurality of BSSs connected via the DS 80 is called an extended serviceset (ESS). STAs included in the ESS may communicate with each other, andthe non-AP STA may move from one BSS to another BSS in the same ESSwhile seamlessly performing communication.

The DS 80 is a mechanism allowing one AP to communicate another AP.Through the DS 80, an AP can transmit a frame for STAs associated to theBSS managed by the AP, transfer a frame when one STA moves to anotherBSS, or transmit or receive frames to and from an external network suchas a wired network. The DS 80 is not necessarily a network. Namely, theDS 80 is not limited to any form so long as it can provide a certaindistribution service defined in IEEE 802.11 standard. For example, theDS 80 may be a wireless network such as a mesh network or a physicalstructure connecting the APs.

Nomenclature in this description is as follows:

-   -   access category (AC): A label for the common set of enhanced        distributed channel access (EDCA) parameters that are used by a        quality of service (QoS) station to contend for the channel in        order to transmit medium access control (MAC) service data units        (MSDUs) with certain priorities.    -   access point (AP): Any entity that has station functionality and        provides access to the distribution services, via the wireless        medium (WM) for associated stations.    -   basic service area (BSA): The area containing the members of a        basic service set (BSS). It may contain members of other basic        service sets.    -   basic service set (BSS): A set of stations that have        successfully synchronized. Membership in a BSS does not imply        that wireless communication with all other members of the BSS is        possible.    -   direct link: A bidirectional link from one non-access point        (non-AP) quality of service (QoS) station (STA) to another        non-AP QoS STA operating in the same infrastructure QoS basic        service set that does not pass through a QoS access point (AP).        Once a direct link has been set up, all frames between the two        non-AP QoS STAs are exchanged directly.    -   enhanced distributed channel access (EDCA): The prioritized        carrier sense multiple access with collision avoidance (CSMA/CA)        access mechanism used by quality of service (QoS) stations        (STAs) in a QoS basic service set. This access mechanism is also        used by the QoS access point (AP) and operates concurrently with        hybrid coordination function (HCF) controlled channel access        (HCCA).    -   network allocation vector (NAV): An indicator, maintained by        each station, of time periods when transmission onto the        wireless medium (WM) will not be initiated by the station        whether or not the station's clear channel assessment (CCA)        function senses that the WM is busy.    -   non-AP quality of service (QoS) station (non-AP QSTA): A station        (STA) that supports the QoS facility, but is not an access point        (AP). A non-AP STA does not have an hybrid coordinator (HC) and        uses the QAP for the distribution system services (DSSs).    -   non-QoS AP (non-QAP) or legacy AP: An access point (AP) that        does not support the quality of service (QoS) facility.    -   non-QoS station (non-QSTA) or legacy non-AP STA: A station (STA)        that does not support the quality of service (QoS) facility.    -   QoS access point (QAP): An access point (AP) that supports the        QoS facility. The functions of a QAP are a superset of the        functions of a non-QAP, and thus a QAP is able to function as a        non-QAP to non-QSTAs.    -   QoS basic service set (QBSS): A basic service set (BSS) that        provides the QoS facility.

An infrastructure QBSS contains a QoS access point.

-   -   QoS station (QSTA): A station (STA) that implements the QoS        facility. A QSTA acts as a non-QSTA when associated in a non-QoS        basic service set.    -   service period (SP): A contiguous time during which one or more        downlink unicast frames are transmitted to a QSTA and/or one or        more transmission opportunities (TXOPs) are granted to the same        STA. SPs can be scheduled or unscheduled. For a non-AP STA,        there can be at most one SP active at any time.    -   scheduled SP: The SP that is scheduled by the QAP. Scheduled SPs        start at fixed intervals of time.    -   unscheduled SP: The period that is started when a non-AP QSTA        transmits a trigger frame to the QAP.    -   medium access control (MAC) protocol data unit (MPDU): The unit        of data exchanged between two peer MAC entities using the        services of the physical layer (PHY).    -   medium access control (MAC) service data unit (MSDU):        Information that is delivered as a unit between MAC service        access points (SAPs).    -   traffic category (TC): A label for medium access control (MAC)        service data units (MSDUs) that have a distinct user priority        (UP), as viewed by higher layer entities, relative to other        MSDUs provided for delivery over the same link. Traffic        categories are meaningful only to MAC entities that support        quality of service (QoS) within the MAC data service. These MAC        entities determine the UP for MSDUs belonging to a particular        traffic category using the priority value provided with those        MSDUs at the MAC service access point (MAC_SAP).    -   traffic stream (TS): A set of medium access control (MAC)        service data units (MSDUs) to be delivered subject to the QoS        parameter values provided to the MAC in a particular traffic        specification (TSPEC). TSs are meaningful only to MAC entities        that support QoS within the MAC data service. These MAC entities        determine the TSPEC applicable for delivery of MSDUs belonging        to a particular TS using the TS identifier (TSID) value provided        with those MSDUs at the MAC service access point(MAC_SAP).    -   traffic classification (TCLAS): The specification of certain        parameter values to identify the medium access control (MAC)        service data units (MSDUs) belonging to a particular traffic        stream (TS). The classification process, performed above the MAC        service access point (MAC_SAP) at a QoS access point, uses the        parameter values for a given TS to examine each incoming MSDU        and determine whether this MSDU belongs to that TS.    -   traffic identifier (TID): Any of the identifiers usable by        higher layer entities to distinguish medium access control (MAC)        service data units (MSDUs) to MAC entities that support quality        of service (QoS) within the MAC data service. There are 16        possible TID values; 8 identify TCs, and the other 8 identify        parameterized TSs. The TID is assigned to an MSDU in the layers        above the MAC.    -   traffic specification (TSPEC): The quality of service (QoS)        characteristics of a data flow to and from a non-AP QSTA.    -   tunneled direct link setup (TDLS): A protocol that uses a        specific Ethertype encapsulation to tunnel direct link setup        frames through an AP, to establish a direct link.    -   TDLS initiator: STA that transmits a TDLS Setup Request frame.    -   TDLS peer STA: STA with which a direct link has been established        or is being established using the TDLS protocol.    -   peer unscheduled automatic power save delivery (U-APSD): A power        save mode based on 35 unscheduled service periods that may be        used between two STAs that have setup a direct link using TDLS.    -   peer power save mode (PSM): A power save mode based on scheduled        service periods that may be 38 used between two STAs that have        setup a direct link using TDLS.    -   peer unscheduled automatic power-save delivery (U-ASPD): A power        save mode based on un scheduled service periods between two STAs        that have setup a direct link using TDLS.    -   TDLS sleep STA: A TDLS peer STA that is in power save mode using        Peer U-APSD.    -   TDLS buffer STA: A TDLS peer STA that buffers traffic for a TDLS        sleep STA.

TDLS is characterized by the use of signaling frames that areencapsulated in data frames so that the signaling frames can betransmitted through an AP transparently. This means that the AP does notneed to be direct link aware, nor does it have to support any of thecapabilities which will be used on the direct link.

The WLAN system which implements the embodiments of the presentinvention supports TDLS. Hereinafter, a TDLS peer STA, a TDLS sleep STAand a TDLS buffer STA may be referred to as a peer STA, a sleep STA anda buffer STA, respectively. A STA is regarded as a non-AP STA unlessthere is any explicit different explanation in this description.

Even non-AP STAs associated with a legacy AP can set up a TDLS link as adirect link therebetween and tear down the direct link. In order that aSTA sets up or tears down the TDLS link with a peer STA, the STA and thepeer STA can exchange management frames through the legacy AP. However,the legacy AP cannot be directly involved in allowing two non-AP STAs toset up the TDLS link. To solve such a problem, encapsulated the TDLSframes are transmitted to the peer STA through the legacy AP. The legacyAP performs only a function of relaying the communication between thenon-AP STAs and is not involved in setting up, tearing down, andmanaging the TDLS link. An embodiment described later can be usefullyapplied to the TDLS wireless network in which the TDLS framesencapsulated in the form of a data frame are transmitted for the purposeof setting up, tearing down, and managing the TDLS link.

The non-AP STA supports PSM in the TDLS. The PSM may be based on peerU-APSD. Support for Peer U-APSD means that the STA has the capability tobuffer frames for the peer STA that operates in Peer U-APSD, and todeliver them during unscheduled service periods. A buffer STAtemporarily buffers data for a peer sleep STA in the PSM and transmitsthe buffered data to the peer STA through the TDLS link. The sleep STAcan enter into the PSM without tearing down the TDLS link. The sleep STAcan receive the data buffered in the buffer STA through the TDSL link.

FIG. 2 is a diagram illustrating an example of a TDLS frame. A TDLSframe is a data frame which includes encapsulated TDLS managements suchas TDLS setup, TDSL tear down, etc. A STA transmits the TDLS frame to apeer STA through a legacy AP. The TDLS frame includes a MAC header field110, a logical link control (LLC)/sub-network access protocol (SNAP)field 120, a remote frame type field 130, a TDLS packet type field 140,and an information field 150.

The MAC header field 110 may include a frame control field, aduration/ID field, plural address fields (Address1, Address2, Address3,and Address4), a sequence control field, and/or a QoS control field. Theframe control field includes a power management field indicating whetherit operates in a PSM. The power management field of the frame controlfield indicates a mode in which the STA operates after exchange of aseries of frames. The power management field is used to indicate thepower management mode of a STA. The value of this field remains constantin each frame from a particular STA within a frame exchange sequencedefined in 9.12. The value indicates the mode in which the station willbe after the successful completion of the frame exchange sequence. Avalue of 1 indicates that the STA will be in PSM. A value of 0 indicatesthat the STA will be in active mode.

The QoS control field in the MAC header field 110 serves to identify atraffic category (TC) or a traffic stream (TS) to which the framebelongs and a variety of QoS-related information of the frame whichvaries depending on the frame type and the sub-frame type.

The LLC/SNAP field 120 includes an LLC/SNAP header. The remote frametype field 130 can be set to a value (for example, “2”) indicating aTDLS frame.

The TDLS packet type field 140 is set to a value for specifying the typeof the TDLS frame. Examples of the type of the TDLS frame and the valuecorresponding thereto are shown in Table 1.

TABLE 1 Field Value Meaning 0 TDLS Setup Request 1 TDLS Setup Response 2TDLS Setup Confirm 3 TDLS Teardown 4 TDLS Peer Traffic Indication 5 TDLSChannel Switch Request 6 TDLS Channel Switch Response 7 TDLS Peer PSMRequest 8 TDLS Peer PSM Response

FIG. 3 is a diagram illustrating a communication method according to anembodiment of the present invention.

To establish a direct link, a STA1 310 which is a TDLS initiatortransmits a TDLS request frame to a STA2 320 which is a peer STA (S300).The TDLS request frame is a TDLS frame which the TDLS packet type field140 in the TDLS frame is set to a value ‘0’. The TDLS request isencapsulated in a data frame and is then transmitted. The AP 350 relaysthe TDLS request frame to the STA2 320 as a data frame.

The STA2 320 transmits a TDLS response frame to the STA1 310 via a AP350 (S310). If STA2 320 accepts the TDLS setup request, STA2 320 respondwith the TDLS response frame with a status ‘successful’. If STA2 320declines the TDLS setup request, STA2 320 respond with the TDLS responseframe with a status ‘declined’. If no TDLS Setup Response frame isreceived within a certain interval, the TDLS initiator 310 mayterminates the setup procedure.

The STA1 310 sends a TDLS setup confirm frame to the peer STA 320 toconfirm the receipt of the TDLS Setup Response frame.

After establishing TDLS, STA1 and STA2 can exchange traffic data throughthe direct link. During TDLS setup procedure, STA1 and STA2 can exchangesupport of peer U-APSD. Support for peer U-APSD means that the STA hasthe capability to buffer frames for the peer STA that operates in PeerU-APSD, and to deliver them during unscheduled service periods. Asubfield in the TDLS setup request frame and/or the TDLS setup responseframe may be set to indicate the support of peer U-APSD.

The STA2 320 enters PSM (S330). The STA2 320 may enter PSM by settingthe power management field in the frame control field of an acknowledgedMAC protocol data unit (MPDU) transmitted to the peer STA over thedirect link. The STA2 320 notifies the STA1 310 of entering of PSM. Aframe which includes the power management field set acts as an indicatorindicating that the STA2 320 enters PSM. The STA that transmitted theframe with the power management field set is referred to as a sleep STA.The STA receiving the frame with the power management field set isreferred to as a buffer STA. In this embodiment, it is shown that STA1310 is a buffer STA and STA2 320 is a sleep STA. Otherwise, the STA2 320may be a buffer STA and the STA1 310 may be a sleep STA. A sleep STA maybe a buffer STA at the same time.

The buffer STA 310 buffers received traffic data frames (e.g. MSDUs)destined for the sleep STA 320 (S340).

The buffer STA 310 transmits a peer traffic indication (PTI) frame tothe sleep STA 320 through the AP 350 (S350). The PTI frame is a TDLSframe which the TDLS packet type field 140 in the TDLS frame is set to avalue ‘4’. The PTI is encapsulated in a data frame and is thentransmitted. The PTI indicates the state of the power save buffer at thebuffer STA 310 that is buffering data for a Peer STA 320 in PSM. Table 2shows an example of information for the PTI frame.

TABLE 2 Field Notes Category This field represents TDLS Action Thisfield represents TDLS peer traffic indication AC_BK traffic set to 0 ifAC_BK is empty and set to 1 if traffic is available available in AC_BK.AC_BE traffic set to 0 if AC_BE is empty and set to 1 if traffic isavailable available in AC_BE. Values 2-255 are reserved AC_VI trafficset to 0 if AC_VI is empty and set to 1 if traffic is availableavailable in AC_VI. AC_VO traffic set to 0 if AC_VO is empty and set to1 if traffic is available available in AC_VO. Link Identifierinformation that identifies the direct link TID indicate the highest TIDfor which the peer STA has buffered traffic. Sequence Control TheSequence Control field is set to the sequence number of the latest MPDUtransmitted to the sleep STA to which the PTI frame containing thiselement is addressed, from the TID indicated in the TID field. If aservice period must always be triggered, the field is set to the highestvalue.

In the IEEE 802.11e standard, there are four kinds of AC: AC_BErepresents best effort, AC_BK represents background, AC_VI representsvideo and AC_VO represents voice. The PTI frame can indicate thenon-empty AC(s) by setting the corresponding AC Traffic Availablesubfield to 1. The TID field can be set to the highest TID for which thepeer STA has buffered traffic. The sequence control field can be set tothe sequence number of the latest MPDU from the TID indicated in the TIDfield that has been transmitted to the sleep STA to which the PTI framecontaining this element is addressed. If a service period must betriggered, the sequence control field may be set to the highest sequencenumber value.

The buffer STA 310 transmits the PTI frame to the sleep STA 320 if thefollowing conditions are met: (1) a new frame arrives at the PU bufferSTA, the new frame being destined for the sleep STA, (2) the framebuffer at the buffer STA contains no other frames with the same AC thatare destined for the sleep STA, and (3) no SP has occurred for that ACand for the sleep STA, for a certain interval prior to the arrival ofthe new traffic.

The sleep STA 320 sends a trigger frame to the buffer STA 310 (S360).When the sleep STA 320 receives the PTI frame indicating that frames arebuffered at the buffer STA 310 for one or more ACs, and the sleep STA320 has not received from the buffer STA 310 an MPDU with a TID asindicated in the TID field of the PTI frame with a higher sequencenumber than the sequence number as indicated in the sequence numberfield in the sequence control field of the PTI frame, the sleep STA 320can initiate an unscheduled SP with the buffer STA to retrieve thebuffered MSDU(s) for the AC(s) for which no unscheduled SP is currentlyactive.

The trigger frame indicates that the sleep STA 320 in the PSM wakes upand the power management mode is changed into active mode. The triggerframe may be a null data frame of which the power management bit fieldis set to “0” (value indicating the active mode). The trigger frame mayfurther include information on the transmission path (direct link orother link) through which the sleep STA 320 hopes to receive the dataframe from the buffer STA 310.

The buffer STA 310 received the trigger frame transmits one or morebuffered traffic frame to the sleep STA 320 through the direct link(S370).

The sequence control field and the TID field in the PTI frame is used toprevent unnecessary allocation of SP due to invalid PTI transmission.

FIG. 4 is a diagram illustrating a problem due to invalid PTItransmission. A buffer STA 410 sends a first PTI frame to a AP 450(S400). For any reason, the AP 450 may delay the relay of the first PTIframe. After a certain interval, the buffer STA 410 which does notreceive any triggering of SP sends a second PTI frame to a AP 400(S410). The second PTI frame is a duplication of the first PTI frame.The AP relays the first PTI frame to a sleep STA 420 (S420). The sleepSTA allocates a first SP for the first PTI frame (S430). Allocation ofSP means the sleep STA changes its power management mode into activemode and sends a trigger frame to the buffer STA 410. The AP relays thesecond PTI frame to a sleep STA 420 (S440). The sleep STA allocates asecond SP for the second PTI frame (S450).

The first SP and the second SP are allocated for same traffic. Thesecond SP is a duplicated SP and unnecessary radio resource.

To prevent unnecessary allocation of SP, the sleep STA 420 determinesthe duplication of PTI transmission by using the sequence control fieldand the TID field in the PTI frame. When the sleep STA 420 has notreceived from the buffer STA 410 an MPDU with a TID as indicated in theTID field of the PTI frame with a higher sequence number than thesequence number as indicated in the sequence number field in thesequence control field of the PTI frame, the sleep STA 420 allocates SP.For above cases, since the sleep STA 410 receives traffic through thefirst SP for the first PTI frame, the sleep STA 420 does not allocatesthe second SP for the second PTI frame. As a result, efficiency of radioresource allocation can be improved.

FIG. 5 is a block diagram of an apparatus for wireless communication toimplement an embodiment of the present invention is implemented. Anapparatus 500 may be a buffer STA or a sleep STA. The apparatus 500includes a processor 510, a memory 520 and an RF (Radio Frequency) unit530. The processor 510 implements a proposed function, process and/ormethod. Power management and TDLS setup can be performed by theprocessor 510. The memory 520 is operatively connected to the processor510 and stores information for operating the processor 510. The RF unit520 is operatively connected to the processor 510 and transmits and/orreceives RF signals.

The processor 510 may include application-specific integrated circuit(ASIC), other chipset, logic circuit and/or data processing device. Thememory 520 may include read-only memory (ROM), random access memory(RAM), flash memory, memory card, storage medium and/or other storagedevice. The RF unit 530 may include baseband circuitry to process radiofrequency signals. When the embodiments are implemented in software, thetechniques described herein can be implemented with modules (e.g.,procedures, functions, and so on) that perform the functions describedherein. The modules can be stored in memory 520 and executed byprocessor 510. The memory 520 can be implemented within the processor510 or external to the processor 510 in which case those can becommunicatively coupled to the processor 510 via various means as isknown in the art.

In view of the exemplary systems described herein, methodologies thatmay be implemented in accordance with the disclosed subject matter havebeen described with reference to several flow diagrams. While forpurposed of simplicity, the methodologies are shown and described as aseries of steps or blocks, it is to be understood and appreciated thatthe claimed subject matter is not limited by the order of the steps orblocks, as some steps may occur in different orders or concurrently withother steps from what is depicted and described herein. Moreover, oneskilled in the art would understand that the steps illustrated in theflow diagram are not exclusive and other steps may be included or one ormore of the steps in the example flow diagram may be deleted withoutaffecting the scope and spirit of the present disclosure.

What has been described above includes examples of the various aspects.It is, of course, not possible to describe every conceivable combinationof components or methodologies for purposes of describing the variousaspects, but one of ordinary skill in the art may recognize that manyfurther combinations and permutations are possible. Accordingly, thesubject specification is intended to embrace all such alternations,modifications and variations that fall within the spirit and scope ofthe appended claims.

The invention claimed is:
 1. A method of managing power save in awireless network, the method comprising: establishing, by a station(STA), a direct link with a peer STA by exchanging a Tunneled DirectLink Setup (TDLS) setup request frame and a TDLS setup response framevia an access point (AP); transmitting, by the STA via the direct link,an indicator indicating that the STA enters a power save mode (PSM);entering, by the STA, the PSM; and receiving, by the STA, a peer trafficindication (PTI) frame from the peer STA, the PTI frame indicating thattraffic data destined for the STA is buffered by the peer STA; whereinthe PTI frame includes a sequence control field indicating a sequencenumber of a latest data unit transmitted to the STA; and an accesscategory (AC) traffic available field indicating whether bufferedtraffic associated with a predetermined AC is present.
 2. The method ofclaim 1, wherein the PTI frame further includes information thatidentifies the direct link.
 3. The method of claim 1, wherein: theindicator includes a power management field in a frame control field ofa frame; and the PSM is entered after transmitting the power managementfield.
 4. The method of claim 1, wherein the TDLS setup request frameand the TDLS setup response frame are encapsulated in data frames inorder to allow the TDLS setup request frame and the TDLS setup responseframe to be transmitted transparently through the AP.
 5. An apparatusfor supporting Tunneled Direct Link Setup (TDLS), the apparatuscomprising: a radio frequency (RF) unit configured to transmit andreceive radio signals; and a processor operatively coupled with the RFunit and configured to: establish a direct link with a peer station(STA) by exchanging a Tunneled Direct Link Setup (TDLS) setup requestframe and a TDLS setup response frame via an access point (AP); transmitan indicator via the direct link, the indicator indicating that theapparatus enters a power save mode (PSM); enter the PSM; and receive apeer traffic indication (PTI) frame from the peer STA, the PTI frameindicating that traffic data destined for the apparatus is buffered bythe peer STA; wherein the PTI frame includes: a sequence control fieldindicating a sequence number of a latest data unit transmitted to theapparatus; and an access category (AC) traffic available fieldindicating whether buffered traffic associated with a predetermined ACis present.
 6. The apparatus of claim 5, wherein the PTI frame furtherincludes information that identifies the direct link.
 7. The apparatusof claim 6, wherein: the indicator includes a power management field ina frame control field of a frame; and the processor is furtherconfigured to enter the PSM after transmitting the power managementfield.
 8. The apparatus of claim 5, wherein the TDLS setup request frameand the TDLS setup response frame are encapsulated in data frames inorder to allow the TDLS setup request frame and the TDLS setup responseframe to be transmitted transparently through the AP.